Compressor unloading mechanism



Nov. 4, 1941. r P A CQNDIT 2,261,911

COMPRESSOR UNLOADING MECHANISM Filed Oct. 3, 1939 2 Sheets-Sheet 1 INVENTOR & 80;! x.

ATTIORNEYS r P. A. CONDIT 2,261,911

COMPRESSOR UNLOADING' MECHANISM Filed odt. 3, 1959 2 Sheets-Sheet? Nov. 4, 1941.

ATTORNEYS Patented Nov. 4, 1941 UNITED STAT as PAT E N T 0 PF ICE ooMPnnsson UNLOADING MECHANISM Paul A. Condit, Mount Vernon, Ohio Application October 3, 1939, Serial :No. 297,663

5 Claims.

maximum down to minimum speed of the prime mover, but for unloading down to an output lower than afforded by such minimum speed, it has been necessary in actual practice to resort to supplementary unloading devices which operated in step by step fashion, with the result that straight line unloading was not achieved in this part of the range. To eliminatesthe above objections it has been proposed to use clearance pockets of variable volume, involving theme of a piston having a screw adjustment to alter the volume of the clearance chamber, but these proposals have not proved out to be practical on account of the high pressures involved.

The present invention accordingly aims to .provide a compressor unloading mechanism wherein the volume of the clearance pocket may be accurately regulated in a practicaland satisfactory manner to conform to operating requirements, and avoiding the objections heretofore met with in practical use. In accordance with "the present invention, in its broader aspects, the volume of the clearance chamber is regulated by introducing into or withdrawing from the chamber as needed, a suitable fluid medium under pressure, preferably liquid such as lubricating oil, the quantity of liquid which is in the clearance chamber at any particular time determining the effective volume of the chamber from the standpoint of the extra clearance which it adds to the cylinder space of the compressor, and therefore theextent of its unloading eifect upon the output of the compressor. The amount of liquid present in the clearance chamber is regulated to conform to operating requirements, and by combining a variable clearance chamber of the above character with speed control, as above mentioned, straight line unloading may be obtained in a practical manner down to 80%, or more. The range of straight line unloading may befurther increased by combiningsucha variable clearance chamber with other supplementary unloading devices. The above and other objects and advantages of the invention will be in part obvious and in part specifically. referred to in the specification hereinafter contained which, taken in conjunction with the accompanying drawings,

discloses certain preferred forms of unloading mechanism whichmay be used in carrying out the invention. From the standpoint of the invention in its broader aspects, however, such disclosure should be considered as merely illustrative of the principles of the invention. In the drawings the eifective clearance volume in. substantially straight line relation to the operating requirements of the compressor.

Fig. 2 is a, central longitudinal section through the clearance chamber showing in greater detail one structural form which the latter may assume, and also-showing in more'detail a pilot control valve'mechanism for the clearance chamber.

Fig. 3 is a detail section taken on the line 3.3

of Fig. 2, looking in the direction of the arrows.

Fig. 4 is a diagrammatic view showing schematically an auxiliary unloading mechanism which may be combined with the clearance chamber to obtain straight line unloading over a greater range.

Fig. 5 is a view similar .toFig. .lbut showing a somewhat modified and simplified form of clearance chamber.

The invention -is illustrated in Figs. 1 and 2 as applied to :a compressor cylinder I having .a piston 2, suction passageway 3 and discharge passageway 4, the clearance chamber hereinafter described being mounted upon the cylinder head -5 of the compressor and in communication with the cylinder space at the .head end of the compressor, through .a .passageway 6 .in the cylinder head 5.

.In the form of the invention shown in Fig. 1 a cylindrical extension 1 extends outwardly from the cylinder head 5 to surround a clearance chamber designated generally by numeral 8, and an end wall 9 fits in and is suitably clamped against the outer end of extension 7.

In accordancewith the present invention the clearance chamber 8 is constructed to provide a portion 8a, into which suitable fluid under pressure may be introduced, and from which such fluid may be withdrawn, whereby the effective volume of what may be termed the clearance phragm portion 81) of the chamber depends upon the admission or withdrawal of fluid under pressure from said chamber 8a.

In the form of the invention under discussion a movable diaphragm I is interposed between the sub-chambers 8a and 8b, to seal off the fluid in sub-chamber 8a from the gases contained within sub-chamber 8b and the cylinder space. The general mode of operation of the unloading mechanism as thus far briefly outlined, will first be given, with subsequent discussion of certain preferred features of construction and mode of operation of the invention in its more specific aspects.

Referring more particularly to Fig. 1, suitable fluid under high pressure, such as lubricating or other oil of similar character, may be supplied to said sub-chamber 8a, through a pipe II, the flow of oil through pipe I I into the sub-chamber being controlled by a suitable valve I2, which may be of the pressure operated type having a dia- I3. The discharge of oil from said chamber 8a maybe controlled by a similar valve I4 having a diaphragm I5, which is interposed in a discharge pipe I6 leading for example to the oil sump of the engine which drives the compressor. Whenever valve I2 is open permitting the introduction of more oil in sub-chamber 8a, diaphragm I0 is moved to the right as shown in Fig. 1, thus reducing the volume of the effective clearance space 8b of the chamber and resulting in a decreased unloading effect upon the head 'end of the compressor; and conversely when valve I4 is open to permit the discharge of oil from said sub-chamber 8a, the gaseous pressure within the compressor cylinder moves diaphragm II] to the left, as shown in Fig. 1, thus increasing the volume of the effective clearance space of sub-chamber 8b, and increasing the unloading efiect thereof upon the compressor. Thus in the embodiment of the invention under discussion the effective clearance volume depends upon the quantity of liquid within sub-chamber 8a, the pressure in pipe II being high enough to overcome the cylinder pressure When it is desired to decrease the unloading effect and the cylinder pressure ejecting liquid from sub-chamber 8a through pipe line I6 when it is desired to increase the unloading effect. By opening and closing the valves I2 and I4 in proper relation to the operating requirements of the compressor as existing from time to time, the volume of the effective clearance space 8b may be increased or decreased in straight line relation to changes in the operating requirements, so as to provide the proper clearance space for any given degree of unloading throughout the range which the clearance chamber affords.

Fig. 1 shows diagrammatically control apparatus appropriate for operating the unloading mechanism in the above manner. In Fig. 1, Il may be understood as a control instrument of suitable type which is responsive to changes in the operating conditions or requirements of the compressor, compressors'being commonly regulated according to such factors as changes in pressure in the suction, or in the discharge, or by so-called torque control. In Fig. 1 the control instrument I1 is indicated by the line I8 as being responsive to changes in pressure in the suction line leading to the compressor, and as producing corresponding changes in pressure of a pneumatic pipe leading through the instrument I1 to a valve 2| of the bellows type, and having a valve plunger 22 forming a part of a pilot valve mechanism hereinafter described in greater detail.

For the present it may be sufiicient to'say that this valve plunger 22 controls communication between a low pressure liquid supply line 23 which may be connected for example to the lubricating oil system of the engine which drives the compressor, and a pipe 24 which leads to the diaphragm I3 of valve I2 and also to a pipe line 25 which leads to the diaphragm I5 of valve M. Plunger 22 also controls communication between the pipes 24 and 25 and vent pipes 26 and 21, which are connected to a discharge pipe 28 leading, for example, to the oil sump of the engine which drives the compressor. The sequence of operation of valve plunger 22 i such that the valves I2 and I4 are connected selectively to the pipe 23 which causes them to open, or to the pipe 28 which causes them to close, with a neutral position of plunger 22 in between, in which both valves I2 and I4 remain closed and connected to pipe 28 while the operating requirements of the compressor remain constant and in balance with the effective clearance provided by sub-chamber 81).

Fig. 2 shows some of the above described operating parts in greater detail, the diaphragm II), for example, being shown as of conical shape, so as to fit closely against the conical wall 5a in the cylinder head 5, and. having a central hub Illa fitting within passageway 6, thus reducing to a minimum the effective clearance volume provided by sub-chamber 81), when the diaphragm is in the position shown in Fig. 2. Th diaphragm I ll may also be provided with an annular skirt I01) and sealing rings I00, engaging with the interior wall of cylinder head extension I, to maintain a fluid-tight joint between sub-chambers 8a and 8b.

Fig. 2 also shows the valve 2I and its plunger 22 as supported by a bracket 2Ia inside of the annular end wall 9, the plunger 22 being received slidably within a barrel 29 having ports spaced along the plunger which are respectively in communication with the oil pressure pipe 23, the pipe 24 leading to the admission valve I2, the vent pipe 26 serving the admission valve I2, the pipe 25 which is used to open the discharge valve I4, and the vent pipe 21 serving the discharge valve.

The end portion of valve plunger 22 is shown (Fig. 2) as provided with an annular passageway 22a between th cylindrical collars 22b in such manner that in the neutral position shown in Fig. 2, the pipe 23 is in communication with neither of the pipes 24 and 25 which lead respectively to the admission and discharge valves, and the pipes 24 and 25 are in communication respectively with the vent ports 26 and 21, so that both of the valves I2 and I4 remain closed. If the pressure in pipe I8 should increase or decrease (thus calling for increased or decreased unloading effect) plunger 22 will move in one direction or the other, thus opening communication from pipe 23 and passageway 22a to one of the pipes 24 and 25, thus opening either admission valve I2 to introduce more oil into sub-chamber 8a while pipe25 remains in communication with pipe 21 so that the discharge valve remains closed, thus decreasing the effective clearance volume of sub-chamber B1), or communication will be opened through pipe 23 of passageway 22a to pipe 25, thus opening the discharge valve I4 and releasing oil from sub-chamber 8a, so that diaphragm I0 moves to the left as shown in Fig. 2, and the effective clearance volume of sub-cham- Preferably the pilot valve mechanism :above referred to is so arranged as to throttle'theflow of oil to or from sub-chamber 8aas the chamber 8b approaches the eilective clearance volume which is appropriate for thethen existing operating requirements, and thereby to minimize loverregulation or hunting. For this purpose the barrel 29 of the pilot valve mechanism may ,be made adjustable in positionaccording to'the position assumed by the diaphragm It, to thereby modify the action of valve plunger .22. As shown in Fig. 2-the barrel .29;is;s1idably supported by .a cylindrical sleeve 3.0 surrounding fit but having a longitudinal slot 3| therein through scribed extend, and barrel $29 is so connected to the diaphragm ID that it moves one way or the other as the diaphragm changeszits position. As shown in Figs. 2 and 3 the barrel 291s connected to diaphragm H! by means of a link 32 .pivotally connected to the barrel and to a crank arm $.33

Thus if diaphragm i is moving toward the left from the position shownin Fig.2, the plunger 22 being then in position tohold ,openithe discharge valve I4, thelinkmechanism. above described will movethe barrel 29 to the left and thereby-throttle the correspondingport openings of the pilot valve mechanism and cause them to close more quickly than would otherwise be thecase, therebypreventing the diaphragm .ID from over-traveling, and bringing it gradually to rest-in its proper new position. The action is similar when :barrel 29 is-moving to the right.

Under certain operating conditions where :the

' diaphragm tends to remain for the most partin intermediate position without traveling to its respective limit positions,1it may be desirable to force the diaphragm to travel through its full operating stroke every now and then, in order'to keep clean its engaging surfaces with theextension 7, and prevent sticking of the diaphragm.

For this purpose, as shown in Fig. 3, a handoperated plunger 48 threaded into .the end of valve mechanism 2i and engageable with theend of plunger 22, maybe provided to supersedeautomatic operation through the medium of ,pipe 28.

Under these conditions a three-wayeock 4 (Fig.

1) in pipe may be turned to vent the pipe-thus freeing valvemechanism 2| from its action and causing the spring 42 of the valve mechanism, which surrounds plunger 22 and engages thedisk .43 fastened to plunger 22,;to force the adjacent end of the plunger '22 up against plunger-40.

Under these conditions adjustment of plunger .48

enables the diaphragm Iii to be manually moved throughout its entire range, in fact the automatic regulation of clearance as above described becomes superseded by manual regulation.

The degree of straight line unloading obtained by apparatus of the character above described, may be increased by combining therewith auxiliary unloading apparatus which comes into play which is inturn pivot- :;1

:matically regulated when :the clearance chamber 28. has been adjusted to aiford'maximum clearance. "For example, ,a step unloading device for the crank end of the compressor may be used in'combination with a clearance chamber as above described at: the

ation. .The step unloading device will tend to cause unloading .to a greater extent :thanrequired, and accordingly the effective clearance volume ,of the subchamber 8b will be reduced :by control apparatus as above described, until the combined effect of the two-unloading devices conforms to operating requirements. And thiscombined unloading efiect will still "vary in straight line relation 3150 changesin theoperatingl-requira ments, up to the maximum degree :of unloading which the two'unloading devices actingtogether will afford, since the clearance chamber .adds .to the unloading eflect of the step unloading device, the additional unloading effect which is :necessary to straight line regulation.

In Fig. 4 I have shown such an arrangement diagrammatically, a variable clearance chamber 44 as above described being used at-the head .end of the compressor cylinder, and step unloading at the crank end of the cylinder being accomplished by a diaphragm or bellows device 45 which acts to hold the compressor suction'valve 46 open, to fully unload .the crank end of the compressor when desired. The devices=45 and :46 will'not be described in detailsince suitable forms thereof are known in :the art, and the variable clearance. chamber 44 maybeunderstoodas; autoin accordance with ;o perating requirements-by avalve 2| having ra-plunger 22, etc., as above described in connection with Figs. 1 to 3.

' operated by means of a v further port 50 In Fig. .4 the unloading device :45-is shown .as

pilot device having a stationary barrel 41havinga port 58wihchis supplied with oil under pressure by pipe 4.9, and a which supplies this oil under pressure through. pipe 5| -to bellows device 45 when .the crank end of the'ficompressor cylinder is to be unloaded. ,A pilot valve member52 connects the ports 48 and 50 when the crank end of the cylinder is to be unloaded, and at: other times vents the port 50 so that suction-valve 4t ofthe compressor operates in the normal way.

The pilot valve :52 maybe controlled by lugs 53 and 54on. plunger ;22, between whichiis positioned an arm 55 extending out from pilot valve '52. The lugs 53 and :54 are so positioned that so lon as operating "requirements call for :a degree of unloading which :is within the range alforded by the variable clearance chamber 4.4, pilot valve 52 remains in .a position in which :the port 50 is vented, so that the unloading device at thecrank end of the cylinder is not in operation. But if operating requirements call for an extent of unloading greater than the maximum afforded by the chamber 44, the plunger 22 will travel to the left .(see Fig. 4) far enough to cause lug 54 to engage arm 55 and move pilot valve 52 to the position shown in Fig. 4, wherein liquid under communicates with chamber needed, plunger 22 will then move tothe right (as shown in Fig. 4) far enough to regulate the effective clearance volume of chamber 44 until the combined unloading effect at the two ends of the cylinder corresponds to operating requirements. If operating requirements should then change so as to fall within the range afforded by chamber 44 acting alone, plunger 22 will move far enough to the right to cause lug 53 to engage arm 55 and thereby move pilot, valve 52 to a position where port 56 is vented and the unloading device at the crank end of the cylinder cut out of operation. Thus by using a variable clearance chamber of the character above described in conjunction with other unloading devices, a straight line unloading effect is obtainable over a greater range.

In Fig. I have shown schematically a somewhat modified form of unloading mechanism which is within the invention in its broader aspects. In this instance a clearance chamber 56 communicates through passageway 51 with a compressor cylinder 58, and a storage tank 59 56 through a pipe 60 having an adjustable orifice 6| therein, in such manner that liquid is interchangeable between the chambers 56 and 59. Thus the effective clearance volume of chamber 56, or the part thereof which is not occupied by liquid, depends upon the relative gaseous pressures existing'in the chambers 56 and 59, and the unloading effect of chamber 56 may be increased or decreased by varying the gaseous pressure in the storage tank 59. A check valve 62 operating between valve seats 63 and 64, may be used to insure that the liquid will not pass into cylinder 58, or gas from the cylinder pass into pipe 60 when chamber 59 is adjusted to maximum clearance. As shown the valve 62 is in the form of a float operating in the perforated tube 65. Gas under pressure may be admitted to tank 59 through a valve 66 similar to the Valve I2 previously described, and released from the tank by a valve 61 similar in function to the valve I4 previously described.

While the invention has been disclosed as carried out by apparatus of certain specific construction as above described, it should be understood that many changes may be made therein Without departing from the invention in its broader aspects, within the scope of the appended claims.

I claim:

1. A compressor unloading mechanism including a chamber having a passageway affording communication to the cylinder space of the compressor, 'means for altering the efiective clearance volume of said chamber to partially unload the compressor in straight line manner, a step unloading device for said compressor, and means for throwing said step unloading device into and out of operation at the limits of the unloading range afforded .by said clearance chamber, thereby to afford substantially straight line unloading effect through the combined unloading range afforded by the clearance chamber and step unloading device.

2. A compressor unloading mechanism including a chamber having a passageway affording communication to the cylinder space of the compressor, means for altering the effective clearance volume of said chamber to partially unload the compressor in straight. line manner, an unloading device of the step type for said compressor, a control member responsive to load requirements of the compressor, said above mentioned means being responsive to operation of said control member, said unloading mechanism being also constructed and arranged to out said stepunloading device into andout of operation at the limits of the unloading range afforded by said clearance chamber and according to the load requirements of the compressor, thereby to obtain a substantially straight line unloading effect through the combined range afforded by said chamber and said step unloading device.

3. A compressor unloading mechanism including a chamber having a passageway affording communication to the cylinder space of the compressor, a movable diaphragm constituting a part of said chamber and having one face thereof exposed to the pressure obtaining in the cylinder space, a control member responsive to load requirements of the compressor, means responsive to operation of said control member for subjecting said diaphragm to fluid pressure opposing the pressure within the cylinder space, and additional means responsive to the position of" said diaphragm for modifying the effect of said control member on said diaphragm.

4. A compressor unloading mechanism including a chamber having a passageway affording communication to the cylinder space of the compressor, a movable diaphragm located in said chamber and dividing the same into a clearance portion and a liquid receiving portion, means'for introducing liquid under pressure into said last mentioned portion of the chamber and withdrawing said liquid therefrom to alter the position of said diaphragm and thereby alter the volume of the clearance portion of said chamber, valve mechanismfor controlling the operation of said last mentioned means including a pilot valve movable in position according to load requirements of the compressor,and a valve seat member cooperating therewith, said valve seat member being movably mounted and linked to said diaphragm to modify the action of said pilot valve member.

5. A compressor unloading mechanism including a chamber having a passageway affording communication to the cylinder space of the compressor, a movable diaphragm located in said chamber and dividing said chamber into a clearance portion and a liquid receiving portionjthereby to subject one face of said diaphragm to cylin der pressure and the other face of said diaphragm to the pressure of liquid in said liquid receiving portion, means for introducing liquid under pressure into said liquid receiving portion of said chamber and for withdrawing liquid from said liquid receiving portion whereby the introduction into and withdrawal of liquid from said liquid receiving portion acting in opposition to the cylinder pressure, determines the position of said diaphragm in said chamber and the effective volume of the clearance portion of said chamber.

PAUL A. CONDIT. 

